N Latex FLC serum free light-chain assays in patients with renal impairment.

The aim of this study was to establish ranges for N Latex free light-chain (FLC) monoclonal-based nephelometric assays in patients with renal impairment. In this retrospective study, serum samples from 284 patients with chronic kidney disease (CKD) stages 1-5 were measured with N Latex and Freelite FLC reagents on the Siemens BNII system and compared with controls without renal impairment. Both κFLC and λFLC concentrations increased with the N Latex FLC and the Freelite assays with each increment in CKD stage. No difference was found in FLC κ concentrations between the two methods. In patients with renal failure, N Latex FLC detected higher concentrations of λFLC (CKD5 median, 128 mg/L; 95% range, 43-302) compared with Freelite (89.5 mg/L, 35-197) (p <0.0001). This resulted in significantly different κ/λ ratios in patients with CKD for the two tests. The Freelite κ/λ ratio in the CKD5 group (median, 1.22; min-max, 0.22-2.70) was significantly increased compared with healthy controls (p <0.0001), and several individual samples were outside the reference range for healthy controls (0.26-1.65). In contrast, none of the 284 patients with CKD had an FLC κ/λ ratio exceeding the N Latex reference limits for healthy controls (0.31-1.56). The N Latex FLC κ/λ ratio in the CKD5 group (0.69, 0.32-1.54) was significantly lower compared with the control group (p <0.0001). These findings demonstrate that the N Latex FLC κ/λ ratio in patients with renal failure did not differ from the reference limits for healthy controls